When on gnome 2 I was used to put .xdg-volume-info files on my removable drives root to set custom drive name and icon. This never worked in xfce, a long ago I asked on the forum: http://forum.xfce.org/viewtopic.php?id=6074 , but gnome bug cited there https://bugzilla.gnome.org/show_bug.cgi?id=551403 is still unconfirmed ... Right now I'm on xubuntu trusty and I just always see generic drive icons, while when on quantal, I've seen the custom icon in notification bubbles ...
The references are pretty old and the bug seems to have gone nowhere. Thunar does not even support custom icons for folders. Closing.